The first 1,000 characters are the "critical mass." After you master these, learning the next 1,000 becomes exponentially easier because you recognize the radicals (building blocks) inside the complex characters.
The book you are looking for is likely , a visual guide that uses illustrations and mnemonic phrases to help learners memorize 1,000 essential Japanese characters. While this specific title is a copyrighted commercial product, there are several legal alternatives and "free to borrow" digital versions of similar 1,000-kanji visual guides available online. Visual Kanji Resources (Free & Legal) understanding through pictures 1000 kanji pdf free work
Search for (a classic book, sometimes free sample chapters) or “Visual Kanji 1000 PDF” on Japanese teaching forums like WaniKani Community or Reddit r/LearnJapanese . Many users share self-made visual guides. The first 1,000 characters are the "critical mass